A $57,000-a-year Connecticut prep school has revealed that several of its teachers abused students for decades.

Four teachers 'more likely than not' engaged in sexual misconduct between the 1970s and 2000s, at the Pomfret School in northeastern Connecticut, according to a letter sent on Monday to the school community.

Pomfret Head of School J Timothy Richards and board of trustees Chairman Justin P Klein signed the letter, which detailed the results of an independent investigation into the misconduct. Richards once worked at St George's School in Rhode Island, where dozens of students were also found to have been abused by teachers.

At Pomfret, one case happened in the early 1970s, one in the 1980s, one spanned the 1980s to early 1990s and the fourth happened after 2000, the report said.

The Pomfret School in northeastern Connecticut (pictured) announced on Monday that four teachers 'more likely than not' engaged in sexual misconduct between the 1970s and 2000s

Pomfret Head of School J Timothy Richards (left) and board of trustees Chairman Justin P Klein (right) signed the letter, which detailed the results of an investigation into the misconduct

The letter said investigators also received nine other reports involving allegations ranging from boundary violations to sexual misconduct.

'In most of these instances, the investigators found the reports credible, but found that there was insufficient information to complete the investigation or were unable to make a finding by a preponderance of the evidence or concluded that the allegation was unsubstantiated,' the letter said.

Pomfret, a boarding and day school located in the namesake Connecticut town, has existed for 122 years. It has 350 students from grades 9 to 12, as well as postgraduates.

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The school did not identify the teachers, but it said some received positive recommendations when they left and some are still working with students.

'The school regrets that these letters of support were written for adults who had clearly violated core community standards of behavior,' Richards and Klein wrote.

They believe two teachers who are alleged to have engaged in sexual misconduct at Pomfret are currently working with children elsewhere, Karen Schwartzman, a spokeswoman for Pomfret, said.

The school told state police but wouldn't identify the schools where the teachers are working, Schwartzman added.

In several cases, Pomfret officials were aware of misconduct, but no one reported the allegations to authorities, the letter said.

Richards once worked at St George's School in Rhode Island (pictured), where dozens of students were also found to have been abused by teachers

All allegations that should have been reported have now been relayed to the Connecticut Department of Children and Families, Schwartzman said. She did not say how many cases were reported.

There is an active investigation into allegations of past sexual misconduct at the school, according to Trooper Kelly Grant, a spokeswoman for Connecticut State Police. She did not know how many cases were involved.

Pomfret is the latest elite boarding school to confront allegations of sexual abuse.

An independent report released earlier this month found dozens of students at Rhode Island's St George's School were abused by school staff from the 1970s to as recently as 2004.

Pomfret's head of school, Richards, was previously an administrator at St George's and has acknowledged not reporting the 2004 allegations to authorities.

Three students told Richards that a teacher at St George's 'was touching them in ways that made them uncomfortable'. Richards and headmaster Eric Peterson interviewed the students.

The accused teacher was placed on leave but later returned to teaching, according to the Boston Globe. Authorities were not notified.

Richards said Peterson told him that 'outside counsel' had found the school wasn't required to alert authorities, the Boston Globe wrote.

He later apologized in a letter sent as Pomfret's head of school. 'I should have known,' Richards wrote. 'I would certainly file that report today, and would expect the same from all Pomfret employees.'

Pomfret (pictured), a boarding and day school located in the namesake Connecticut town, has existed for 122 years. Boarding school tuition is $57,000 per year

Richards worked at St George's for 23 years and moved on to Pomfret in 2011. Peterson, meanwhile, announced in June that he would step down as headmaster.

Other schools where abuse has surfaced include Phillips Academy in Andover, Massachusetts , and Phillips Exeter Academy in New Hampshire.

Boarding school tuition at Pomfret is $57,000 per year. The private high school's alumni include Nobel Prize-winning biochemist James Rothman and Prince Lorenzo Borghese of ABC's 'The Bachelor'.

The letter from Pomfret also noted that an outside attorney had done a comprehensive review of its practices and policies.

It said it has a new team to evaluate abuse allegations, and also requires adults and students to undergo training with experts in the field.

'If a matter arises from our student body today or in the future, we are in a much better position to respond,' the letter said.

If any new reports emerge, the school leaders pledged to 'investigate each matter fully, and respond with both empathy and transparency.'